I expect that she uses a card that earns some type of rewards?
If she opts for Delta Reserve she will earn Skymiles rather than Membership Rewards points. Is that where you want to go with your points? (I am finding Virgin Atlantic Flying Club miles better than Skymiles for domestic Delta flights.)
Adding her as an Additional Cardholder on your Platinum card opens up the ability to transfer to her frequent flyer accounts.
Actually she only uses a business debit card now, which I'm trying to get her away from. The expenses aren't typically enough that she's worried about the reward points, this is more a balance of lounge perks in our household, and if she should earn MRs into our family account as an AU, or get DL baggage in economy (if we ever miss FO again), plus the BOGO F tickets once a year upon renewal.